Vibration problem

Hi,

I'm trying to control the dephasing angle of 4 vibrating tables which are causing us a lot of building vibration. I got an encoder and am calculating the time it takes for each rotation of all 4 tables. First, I actually reached the point where all 4 tables run same speed. Then, i need to incremnt or decrement the angle between them so that the vibration coming from high frequency are either in phase or not. Anyone has and idea or example for that kind of stuff...

Never done anything like that before.

A suggestion would be to put an accelerometer somewhere in/around the system, use this as an indication of the energy. Then use a PID on some phase correction output, to minimize energy.

PID is not fast enough... we're talking about a FAST Task involving 1ms PLC scan...

What frequency are your tables turning at?

around 62 Hz

The following may be a solution! But I'm just guessing really.

In your code each scan you could sequentially increase the speed of the table in question by 1Hz, turning it back to the previous value upon the next scan and then iterating. You could do this until the average energy goes to some predefined value.

You'd probably have to add a little deadtime to the iteration though.

Either that or you could do FFT on the response from the accelerometer (after filtration ofc), and adjust the motors as above until you get sufficient power in the motorfreq*4 harmonic.